1. Field of the Invention
This invention relates to a method of reducing an undesired multiple-echo signal in ultrasound imaging. This invention also relates to an apparatus for reducing an undesired multiple-echo signal in ultrasound imaging.
2. Description of the Related Art
A general ultrasound imaging apparatus includes a probe for emitting an ultrasound beam into a body to be examined. The probe also receives ultrasound echoes from the body.
A typical ultrasound probe of a mechanical scan type includes a transducer, a rotor, and an acoustic window. The transducer is mounted on the rotor. The transducer moves together with the rotor. The acoustic window forms a part of a probe casing in which the rotor and the transducer are disposed. The combination of the rotor and the transducer is spaced from the acoustic window. The probe contains ultrasound propagation medium or liquid which fills a space between the acoustic window and the combination of the rotor and the transducer. The transducer emits an ultrasound beam. The ultrasound beam travels through the propagation liquid and the acoustic window before entering a body to be examined. The transducer receives ultrasound echoes from the body via the acoustic window and the propagation liquid. As the rotor rotates, the direction of the travel of the ultrasound beam emitted from the probe moves so that the body is scanned by the ultrasound beam.
In the typical ultrasound probe, a portion of the ultrasound beam tends to travel between the acoustic window and the transducer while being periodically reflected at the surfaces thereof. Such a phenomenon causes undesired multiple echoes which result in artifact in imaging.
Japanese published unexamined patent application 6-181923 discloses an ultrasound imaging apparatus designed to reduce or weaken a multiple-reflection-caused artifact image. In the apparatus of Japanese application 6-181923, a probe has a heater and a cooler for ultrasound propagation medium therein. In addition, an artifact image is observed via a display. The heater and the cooler are controlled to minimize the intensity of the artifact image indicated on the display. The control of the heater and the cooler adjusts the temperature of the propagation medium, thereby matching the acoustic impedance of the propagation medium and the acoustic impedance of a body to be examined. The heater and the cooler causes a complicated structure of the probe.
Japanese published unexamined patent application 7-178081 discloses an ultrasound imaging apparatus including a received signal processor designed to reduce or weaken multiple-reflection-caused artifact. The received signal processor in Japanese application 7-178081 has a memory previously loaded with an undesired multiple-echo signal. During operation of the apparatus, the received signal processor subtracts the undesired multiple-echo signal from a received signal to remove multiple-reflection-caused artifact. The apparatus of Japanese application 7-178081 requires a process of preliminarily generating an undesired multiple-echo signal, and a process of storing the generated undesired multiple-echo signal into the memory. Such processes tend to be troublesome.